Nomada genus bees have a lot of unlovable qualities. They not only steal food stores from pollinating bees, but they eat their larvae. Then there’s the cannibalism. Yet, these clever and colorful bees are an important part of, if you will, the bee-cosystem.
Nomada bees look like wasps. Because they don’t have to gather food for their own nests, they don’t have pollen-trapping hairs on their legs or bodies. When you see them on flowers, like this one on Indian plum (Oemleria cerasiformis), they’re eating nectar for themselves, not collecting pollen for offspring.
Many local Nomada bees are red, sometimes with yellow or white spots on the abdomen. While they stand out on white flowers and green leaves, the red may help disguise them on brown ground (note: this is my own speculation). They need to be stealthy on the dirt because these are cuckoo bees. They don’t dig their own nests, but they leave their eggs next to the eggs of ground-nesting solitary bees, usually in the Andrena genus.
The Nomada eggs develop just a little faster than the host eggs. The subsequent larvae grow long, scythe-like mandibles, which they first use to kill and eat any other Nomada grubs. In this bee-style Survivor competition, the last living Nomada eats the host larva as a final prize, before consuming the pollen ball the host female provided.
It’s a fierce and opportunistic life, but it’s a niche many species have filled. Bryan Danforth says, in The Solitary Bees, 13% of all bees and 20% of Apidae family bees are brood parasites like Nomada. Keep in mind, to sustain a population of these house-robbing cleptoparasites, there must be a much stronger population of the host bees.
Many online sources mention that male Nomada bees secrete the exact same chemical as the host Andrena bees. Equally fascinating, males transfer this scent to female Nomada by intertwining their antennae during mating. The masking “perfume” then allows the females to better sneak into the host nests, and perhaps get away with claiming they forgot their own address.
While remarkable and true, the link between male Nomada scents and Andrena ground bee chemicals was documented one time by researchers in Europe in 1977 and no one has looked into it since. And if you ever see a mating pair of Nomada, pull out your phone and film it… the antennae winding behavior wasn’t witnessed and published until 2018!
See more of Karen’s work here.
Research on male Nomada bees imitating host bee scents: https://www.science.org/doi/pdf/10.1126/science.196.4294.1117. Accessed 3/15/22.
Antennal grabbing and Nomada courtship: https://pdfs.semanticscholar.org/b375/8a8bacd18baeff6b648b6cc47e96daa39b9a.pdf. Accessed 3/15/22.
Danforth, B.N., et. al, The Solitary Bees: Biology, Evolution, Conservation. Princeton University Press, 2019. https://press.princeton.edu/books/hardcover/9780691168982/the-solitary-bees.